The long-term goal of this proposal is to provide the scientific community with a new array of ultra-thin electrodes that can be chronically implanted in a primate brain and be used to study networks of neurons over long periods of time. This new array provides excellent recording isolation, excellent recording stability, minimum tissue damage (neurons can be isolated within the same piece of tissue for years) and the ability to sample neighboring cells of different types and somata sizes. The array has multiple, closely-spaced, ultra-thin electrodes that can be independently moved with chronically implanted miniature microdrives. While the array has been successfully used for recording in small animal brains, it requires significant enhancements to allow it to fulfill its potential in the primate brain. The first aim of this proposal is to make the electronic and mechanical parts of these arrays resistant to the large accelerations and forces that they will have to bear while being chronically implanted in a primate brain over long periods of time. The second aim is to provide the array with chronic micromotors that will allow moving the electrodes remotely. The third aim is to increase the number of electrodes without compromising the ability to move the electrodes independently. When these arrays are successfully adapted to the primate brain, they will dramatically increase the scientific productivity that can be achieved during daily recording sessions. At the same time, they will allow each primate to be used more efficiently and fulfill two important goals in animal research: to reduce the number of animals used in each research project and refine their use (it is possible to record from a small piece of tissue over a period of several years).The array developed in this proposal will provide the scientific community with a new, powerful tool to study brain circuitry. A detailed knowledge of this circuitry is essential for the development of treatments for the different neurological and psychiatric disorders that affect the human brain.